For sealing materials used for sealing of portions to be brought into contact with automobile fuels, such as a fuel tank, “fuel oil resistance” to perfectly prevent leak of a fuel oil from a fuel tank or the like is required, and for such materials, a fluororubber has been mainly used.
There is a recent tendency to requirement for globalization (worldwide common specifications) of automobile supply, and in the winter cold district, such as North America, fuel oil resistance, specifically sealing properties at not higher than −40° C., are required. Moreover, from the environmental problem, adoption of diesel fuel has spread mainly in Europe.
To meet these requirements, the present applicant has proposed a fluororubber composition capable of sealing even at not higher than −40° C., and has also proposed a sealing material using the fluororubber composition (patent literature 1).
In recent years, however, even in the sealing parts using the material disclosed in the patent literature 1, there is yet room for further improvement in the sealing properties depending upon the use conditions and the like. Specifically, when the fuel is changed to gas oil (diesel fuel) from the conventional pseudo-gasoline or gasoline, leak occurs in the engine evaluation depending upon the use conditions.
More specifically, the above leak occurs in the thermal load test in which use of the above fuel in automobiles in the extremely low-temperature district is supposed. The thermal load test is a test in which a sealing material is mounted at the position for use, then temporarily allowed to stand at a high temperature, specifically about 120° C., and thereafter sufficiently cooled down to a temperature at which the sealing evaluation is intended to be carried out, followed by evaluation of sealing properties.
In the above test, TR-10 has been used as a substitute indicator in the past, but when gas oil is used as a fuel, this indicator has proved to be inapplicable.